the set comes with enough bulbs for you to change EVERY single bulb in the interior. however, i personally think it is silly to turn the reading lights and vanity mirror lights to a xenon color, because for reading or looking in a mirror, a hyperwhite color is not good. plus, the only ones that turn on when you open the door or hit the middle button on the overhead console (where the map lights are), only some of the lights actually turn on.
i only used enough bulbs for these lights, and there are more than enough bulbs to do an entire additional application with the bulbs i have left. you get all the cool xenon effect when the lights turn on, but also keep the functionality of the other lights when you need them (which dont turn on when you open the door, etc).
and yes, these bulbs use xenon gas
just figured i would help out a fellow fanatic who was interested in the xenon interior bulbs but didnt want to pay a whopping $70 + shipping or whatever it is that they cost (i cant remember).
so, for $40 ($35 + $5 shipping), we split the cost and both get the xenon look
first person to claim them can have them